In cellular communication systems, the optimisation of the use of the limited spectrum resource is one of the most critical network management operations. In cellular communication systems, such as GSM, the geographical area is divided into individual cells thereby allowing reuse of carrier frequencies in different cells sufficiently removed from each other for the co-channel interference to be reduced to acceptable levels. In order, to use the resource efficiently, complex frequency planning operations are performed to allocate frequencies to the individual cells.
An approach which is frequently used to improve frequency reuse in cellular communication systems is to introduce sectorised cells wherein a given base station site effectively supports a plurality of cells through the use of directional antennas. For example, for a given base station site, three sectors may be generated by using three directional antennas angled in different directions (i.e. offset by 120° with respect to each other). Such sectorisation may reduce interference and allow for tighter frequency reuse thereby increasing the overall network capacity.
Capacity and frequency planning is generally based on marginal conditions when the system is operating close to the capacity limit. Indeed, it is generally the object of the frequency planning exercise to optimise performance at the capacity limit in order to maximise the capacity of the system. However, a disadvantage of such an approach is that it may not lead to optimal performance when the system is not operating close to the capacity limit. In particular, the resulting operation tends to be over dimensioned for normal operation during lower loadings. This tends to result in inefficient use of resources at lower loadings and may for example result in increased power consumption and/or interference.
Hence, an improved system would be advantageous and in particular a system allowing increased flexibility, high capacity, reduced power consumption, reduced resource usage and/or improved performance would be advantageous.